Consumers value the ability to see the contents of their packages. Consumers also appreciate the toughness and gloss of containers made from polyester. Because of this combination of attributes, containers made from polyethylene terephthalate (PET) produced by the injection stretch blow molding process (ISBM) are the most common type of transparent container on the market. However, the ISBM process is limited to uniform shapes and cannot produce bottles that contain a through-handle. Handles are desirable in larger bottle sizes, where gripping a round or square container becomes cumbersome. Larger size bottles containing a through handle are believed to be produced only by the extrusion blow molding (EBM) process.
The PET (polyethylene terephthalate) compositions used in the injection stretch blow molding process (ISBM) cannot be easily processed using the extrusion blow molding (EBM) process due to their high crystalline melting points and rapid crystallization rates, which gives them a low melt strength. U.S. Pat. No. 4,983,711 describes totally amorphous or slowly crystallizing copolyester compositions related to PET that are particularly useful in extrusion blow molding processes. These compositions comprise terephthalic acid or DMT (1,4-dimethyl terephthalate) moieties with ethylene glycol residues and 25-75 mole % 1,4-cyclohexanedimethanol residues and 0.05 to 1 mole % of a branching agent. These compositions are particularly desirable for extrusion blow molded beverage containers since they yield containers with clarity, gloss and toughness similar to ISBM PET containers.
Unfortunately, containers made from compositions described by U.S. Pat. No. 4,983,711 can cause problems in the PET recycle stream. Ground flake from these containers can stick to the walls of the dryer or agglomerate with ISBM PET container flake in a dryer set at 140-180° C. Mixing ground flake from these containers into ISBM PET container flake could also result in hazy film, sheet or bottles. It is possible to sort out the compositions described in U.S. Pat. No. 4,983,711 from the PET recycle stream, but a much more desirable solution is to find a material that can be both extrusion blow molded into transparent containers, but will be non-problematic in the PET recycle stream at levels much higher than they will be present in the recycle stream.
Thus, there is a need in the art for a transparent material that will crystallize more slowly than the PET used in injection stretch blown applications so that it can be used in extrusion blow molding and profile extrusion processes and that is also non-problematic in the PET recycle stream. Such a material has a combination of one or more of low haze values, short crystallization half-times, and lack of significant stickiness to manufacturing equipment when being processed.